1. Field of the Invention
The present invention relates to the retransmission of a broadcast wave, and more specifically to a retransmission system for a broadcast wave using an extended radio base station system in mobile communications.
2. Description of the Related Art
Broadcast wave retransmission systems, which are a well-known technology, are provided in places such as behind high-rise buildings, in underground malls, etc., where broadcast waves cannot directly reach. They temporarily receive broadcast waves output from a broadcast station and retransmit the broadcast waves. For example, non-patent document 1 described below discloses a technique of retransmitting a terrestrial digital broadcast.
In mobile communication systems, as described in patent document 1 listed below, an extended radio base station system has been proposed. The extended radio base station system can extend a transmission/reception area with antennas and high-frequency device portions such as radio transmission/reception units and the like by separating from base stations for use in areas such as behind high-rise buildings, in underground malls, etc. where broadcast waves cannot directly reach from outside; this separation of these two portions is performed so that radio waves can be transmitted to a mobile terminal in areas where radio waves cannot reach.
FIG. 1 is a schematic chart of a conventional extended radio base station system that has been extended by separating its high frequency device and antenna portion from the body of its base station, which performs baseband processing and the like, as disclosed by patent document 1.
As shown in FIG. 1, an extended radio base station system 1 is configured by a master base station 2, an extended radio base station 4, and a communication line 9 for connection of the master base station 2 to the extended radio base station 4. Although only one extended radio base station 4 is shown in FIG. 1, there can be a plurality of extended radio base stations 4 for the master base station 2. In the following description, equipment for a master base station and equipment for an extended radio base station can be referred to respectively as the master base station 2 and the extended radio base station 4 so far as misunderstanding can be avoided.
The master base station 2 is configured by the following: a radio transmission/reception device 21, connected to an antenna for mobile communications not shown in FIG. 1, for conversion between high frequency radio signals and baseband signals; a baseband signal processing device 22 for performing signal processing such as spreading a signal at a baseband level; a communication network transmission interface 23 for matching an interface with a mobile communication network 5; a transmission interface 24 for matching an interface with the communication line 9 to and from the extended radio base station 4; and a control unit 25 for control of each of the devices above. In case of no communications are performed from the master base station 2 directly to a mobile terminal, the radio transmission/reception device 21 is not required.
The extended radio base station 4 is configured by a radio transmission/reception device 41 connected to an antenna for mobile communications and a transmission interface 42 for matching an interface with the communication line 9.
As described above, in an area such as a tunnel, the underground portion of a building, etc. where radio waves are cut off by an artificial structure, a mobile telephone cannot be normally used. Also, radio and television sets (mobile units) cannot receive broadcast signals. Although there is presently a system for retransmitting radio waves to parts of the enclosed areas in each system, large-scale construction is required for some retransmission systems, and a heavy load can be imposed in performing it independently. However, there is no superposed system for broadcasting and mobile telephones.
As an example, patent document 2 following describes providing an outdoor antenna of a mobile telephone and a TV receiver for the enhanced indoor communication sensitivity of the mobile telephone and providing an indoor repeater having the function of relaying the mobile telephone signals, but does not describe retransmitting a broadcast wave.
Patent document 3 following describes the sharing of PHS and UHF facilities or the enhancing the sensitivity of an indoor PHS communication wave using house antenna equipment for receiving UHF television broadcast waves, but relates to UHF broadcast waves in a specific band and PHS waves for mobile communications in a specific band, and does not describe retransmitting broadcast waves.
What is described in patent documents 2 and 3 is a device for sharing a household unit, and is not a combination of a plurality of superposed systems as infrastructural social facilities.                [Patent Document 1] Japanese Published Patent Application No. 2005-217982        [Patent Document 2] Japanese Published Patent Application No. 2000-261362        [Patent Document 3] Japanese Published Patent Application No. 2000-341162        
[Non-patent Document 1] Giken Koukai in 2004 “Published Exhibition” Technical Exhibition 24-2 “Terrestrial Digital Broadcast” retransmission technique (http://www.nhk.or.jp/str1/open2004/tenji/t24-2.html)